Bernoulli's Effect on Aviation

It is extremely doubtful that any of the passengers on a routine flight of any regular commercial airline ponder the physical specifics of the flight of their airplane. Some sense of wonder may pass through minds of those passengers who sit in window seats overlooking the aircraft's wings, but unless they happen to be physics enthusiasts, their attempts to explain how the multi-ton steel craft is able to lift off the ground and fly through the air thousands of feet above ground will be incomplete at best.

The explanation, actually, is rather simple and can be found in Bernoulli's theory on the nature of airflow around both the moving and stationery objects. Since the wing of an airplane is curved on top and flattened on the bottom, the physical quality of air moving toward it when the plane is in flight or picking up speed on the runway differ on top from that on the bottom. It takes the knowledge of basic trigonometry to conclude that the upper surface of the airplane wing is larger than the lower surface. Therefore, the air passing the wing would have to travel a longer distance on top than on the bottom. This will result in it stretching thinner on top of the wing, hence the air pressure on top of the wing will be lower than that on the bottom of it. The force pushing the plane upwards will thus be higher than the one pushing it downwards, creating a lift that will carry the plane up.

Of course, the curve in the airplane wing is not the only thing that provides the lift. The tilt of the wing is also important. To increase lift, the side of the airplane wing facing the oncoming airflow is tilted upwards. This way, the air passing underneath the wing is directed downwards. Following the Newton's law, the produced reaction from all the air underneath the wing is to push upwards toward the force exerted on it by the air redirected by the tilt of the wing, thus adding to the airplane's lift.

Taking this theory as the true reason for the existence of lift, a keen observer would ask how is the plane able to descend to land at the end of its trip if the wings are always tilted front plane upwards and are always curved on top. First and the most obvious way to descend would be to reduce speed. The slower airflow will result in the pressure equalization between the air flowing over the wing and that flowing under the wing. It will also reduce the force with which the air column underneath the wing is pushing against it in reaction to the downward push from the tilted front slope of the wing. Both these factors will result in the reduction of lift and the subsequent descend of the aircraft.

Another, more mechanical way to bring the plane lower is to use mobile plates at the rear-facing side of the wing called ailerons. If the ailerons are lifted, the air passing over the top of the wing will create the kind of pressure that will result in a force directed downwards and slightly backwards in relation to the aircraft's straightforward movement.

This, therefore, plays a dual role, simultaneously lowering the plane and reducing its speed, which in turn results in less lift and further descent. Pilots, however, should combine this maneuver with the reduction of speed, otherwise the conflicting forces of the upward push from the lift and the downward pressure from the ailerons may severely degrade the aircraft's flight capabilities or even damage it.